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J. Gago

Publications and source records attributed to J. Gago.

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Astro2020 Activities and Projects White Paper: Arecibo Observatory in the Next Decade

The white paper discusses Arecibo Observatory's plan for facility improvements and activities over the next decade. The facility improvements include: (a) improving the telescope surface, pointing and focusing to achieve superb performance up to ~12.5 GHz; (b) equip the telescope with ultrawide-band feeds; (c) upgrade the instrumentation with a 4 GHz bandwidth high dynamic range digital link and a universal backend and (d) augment the VLBI facility by integrating the 12m telescope for phase referencing. These upgrades to the Arecibo telescope are critical to keep the national facility in the forefront of research in radio astronomy while maintaining its dominance in radar studies of near-Earth asteroids, planets and satellites. In the next decade, the Arecibo telescope will play a synergistic role with the upcoming facilities such as ngVLA, SKA and the now commissioned FAST telescope. Further, the observatory will be actively engaged in mentoring and training programs for students from a diverse background.

astro-ph.IM

Exact cost minimization of a series-parallel system

The redundancy allocation problem is formulated minimizing the design cost for a series-parallel system with multiple component choices whereas ensuring a given system reliability level. The obtained model is a nonlinear integer programming problem with a non linear, non separable constraint. We propose an algebraic method, based on Gröbner bases, to obtain the exact solution of the problem. In addition, we provide a closed form for the required Gröbner bases, avoiding the bottleneck associated with the computation, and promising computational results.

math.OC

An algebraic approach to Integer Portfolio problems

Integer variables allow the treatment of some portfolio optimization problems in a more realistic way and introduce the possibility of adding some natural features to the model. We propose an algebraic approach to maximize the expected return under a given admissible level of risk measured by the covariance matrix. To reach an optimal portfolio it is an essential ingredient the computation of different test sets (via Gröbner basis) of linear subproblems that are used in a dual search strategy.

math.OC

A vanishing theorem for a class of logarithmic D-modules

Let $O_X$ (resp. $D_X$) be the sheaf of holomorphic functions (resp. the sheaf of linear differential operators with holomorphic coefficients) on $X$ (=the complex affine n-space). Let $Y$ be a locally weakly quasi-homogeneous free divisor defined by a polynomial $f$. In this paper we prove that, locally, the annihilating ideal of $1/f^k$ over $D_X$ is generated by linear differential operators of order 1 (for $k$ big enough). For this purpose we prove a vanishing theorem for the extension groups of a certain logarithmic $D_X$--module with $O_X$. The logarithmic $D_X$--module is naturally associated with $Y$. This result is related to the so called Logarithmic Comparison Theorem.

math.AG